Puristussyttymistä

Puristussyttymistä, often translated as "compression ignition" or "autoignition" in English, refers to the phenomenon where a fuel-air mixture ignites spontaneously due to the heat generated by compression alone, without the need for an external spark. This process is fundamental to the operation of diesel engines.

In a diesel engine, air is compressed to a very high pressure, which significantly raises its temperature. Once the piston reaches the top of its stroke, diesel fuel is injected into this superheated air. The high temperature of the compressed air causes the injected fuel to autoignite almost instantaneously. This controlled explosion drives the piston down, generating power.

The concept of puristussyttymistä is distinct from spark ignition, which is used in gasoline engines. In spark ignition, a spark plug creates an electrical arc to ignite the fuel-air mixture. The autoignition temperature of the fuel is a critical factor in puristussyttymistä; fuels with lower autoignition temperatures are better suited for diesel engines. The timing and duration of fuel injection, as well as the compression ratio, are carefully controlled to ensure efficient and complete combustion. While desirable in diesel engines, uncontrolled autoignition in gasoline engines, known as knocking or detonation, is detrimental and can damage the engine.